The present invention relates generally to radiation detectors and methods. More specifically, the present invention relates to flexible radiation detectors, as well as radiation detection assemblies and methods including a radiation detector having multiple photodetectors optically coupled to at least two sides of the detector so as to allow improved scintillation based radiation detection.
Scintillation spectrometers are widely used in detection and spectroscopy of energetic photons and/or particles (e.g., X-rays and gamma-rays). Such detectors are commonly used, for example, in nuclear and particle physics research, medical imaging, diffraction, non destructive testing, nuclear treaty verification and safeguards, nuclear non-proliferation monitoring, and geological exploration.
A wide variety of scintillators are now available and new scintillator compositions are being developed. Among currently available scintillators, thallium-doped alkali halide scintillators have proven useful and practical in a variety of applications. One example includes thallium doped cesium iodide (CsI(Tl)), which is a highly desired material for a wide variety of medical and industrial applications due to its excellent detection properties, low cost, and easy availability. Having a high conversion efficiency, a rapid initial decay, an emission in the visible range, and cubic structure that allows fabrication into micro-columnar films (see, e.g., U.S. Pat. No. 5,171,996), CsI(Tl) has found use in radiological imaging applications. Furthermore, its high density, high atomic number, and transparency to its own light make CsI(Tl) a material of choice for X-ray and gamma-ray spectroscopy, homeland security applications, and nuclear medicine applications such as intra-operative surgical probes and Single Photon Emission Computed Tomography or SPECT.
Scintillation spectrometry generally comprises a multi-step scheme. Specifically, scintillators work by converting energetic particles such as X-rays, gamma-rays, and the like, into a more easily detectable signal (e.g., visible light). Incident energetic photons are stopped by the scintillator material of the device and, as a result, the scintillator produces light photons mostly in the visible light range that can be detected, e.g., by a suitably placed photodetector. Various possible scintillator detector configurations are known. In general, scintillator based detectors typically include a scintillator material optically coupled to a photodetector. In many instances, scintillator material is incorporated into a radiation detection device by first depositing the scintillator material on a suitable substrate. A suitable substrate can include a photodetector or a portion thereof, or a separate scintillator panel is fabricated by depositing scintillator on a passive substrate, which is then incorporated into a detection device.
Improving performance of scintillator detectors is generally of great interest, for example, in order to make scintillation based detectors more useful and capable of filling existing and emerging technical needs. One important performance consideration of particular interest in scintillator detector utilization is light output. More light leads to a higher signal-to-noise ratio (SNR) and, therefore, improved time resolution and higher energy resolution. Thus, increasing light output leads to improved detection power, performance, and overall utility of scintillators.
Generating an increase in light output is currently accomplished by increasing light output from one side of the detector. For example, when a scintillator is formed on an opaque substrate, a known way to improve light output is to deposit a reflective coating on the substrate prior to deposition of the scintillator. Although efficacious in increasing light output from the scintillator surface opposed to the substrate, the process is inefficient for several reasons. First, light needs to travel through the scintillator for an additional distance equal to the thickness of the scintillator plus a fraction (between 0 and 1) of the scintillator thickness. As a result of the increase travel distance, light is lost due, for example, to scattering and absorption in the process. Second, the reflectors themselves are inefficient and do not necessarily reflect all of the light photons in the desired direction. Photons are often reflected into another portion of the scintillator (e.g., neighboring microcolumns), are reflected to a place where they are absorbed, or can be absorbed directly by the reflector.
In addition to improved performance, there is a need for improved manufacturing methods, so as to increase the reliability of the devices and reduce production costs. One such improvement is to decrease breakage of photodetectors during assembly and manufacturing. Typically, when a photodetector is used as a substrate, it needs to be firmly held in a frame and exposed to deposition temperatures. The first coating, whether it is the scintillator material itself or another layer (e.g., resin), adheres to all exposed surfaces in the photodetector, including its delicate electrical contacts. When excess or unwanted material is trimmed or removed, these electrical contacts can be damaged, resulting in a rejected device. The same can occur during handling, e.g., for loading and unloading the photodetector on the holder for scintillator deposition, since the photodetector is easily scratched. When in the holder, which is subject to rotation during deposition, the photodetector can move within the holding frame and be scratched. Moreover, during handling, static electricity can build up and damage the electronics. Thus, such processing/fabrication steps provide an opportunity for damaging the costly photodetector, increasing the overall manufacturing time and costs.
Thus, there is a need for improved techniques and methods, as well as detection assemblies, for greater versatility as well as for improved performance, including for increasing light output of scintillation detectors.